Storage apparatus and control method for storage apparatus

ABSTRACT

A storage apparatus connected to a storage device includes a storage module, a memory for storing data to be copied to the storage device, buffers for temporarily saving the data, redundantly, the saved data stored in one of the buffers being recoverable by the data stored in the rest of the buffers, and a control module for executing, storing the data of write request to the storage module and the memory, copying the data to the storage device, saving the data to the buffer when an using rate of the memory is greater than a predetermined rate, writing the saved data stored in the buffer to the memory when an using rate of the memory is not greater than the predetermined rate, detecting a failure of the buffers, and rebuilding the saved data stored in the one of the buffers based on an using state of the buffers.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2009-239309, filed on Oct. 16, 2009 the entire contents of which are incorporated herein by reference.

FIELD

The embodiments discussed herein are related to a storage apparatus and a control method for the storage apparatus.

BACKGROUND

A device of redundant arrays of inexpensive disks, or a RAID device uses a storage system of distributed cache memory type. The RAID device conventionally uses a redundant configuration including a plurality of control modules that control input and output of data to and from a storage for increasing performance and reliability. Read/write processing of data is executed by each control module from/in a logical volume.

Such a RAID device has a remote copy function that ensures ordering, the function which is so-called advanced copy, for increasing the reliability etc.

FIG. 23 is an illustration explaining the RAID device having the remote copy function that ensures the ordering. FIG. 23 illustrates a storage system including a RAID device (a copy source device) 2301 having control modules #00 and #01, and a RAID device (a copy target device) 2302 having control modules #10 and #11.

Each of the control modules included in each of the RAID devices includes a write only buffer having a buffer and a buffer index table (BIT) storage unit; a buffer set information storage unit that stores information relating to a buffer set; and a storage medium that stores data.

The buffer is divided into a plurality of regions each having a given size. Buffer IDs are respectively assigned to the divided regions. Data stored in the storage medium or data to be stored in the storage medium is temporarily stored in the respective regions. The BIT storage unit stores storage locations of data stored in the buffer, or a BIT that is information including buffer IDs in FIG. 23.

Referring to FIG. 23, (0000) written in a buffer represents buffer data stored in a buffer with a buffer ID of 0000. Also, 0000 written in the BIT represents the buffer ID.

The buffer set information storage unit stores information relating to a buffer set that is a combination of buffer data stored in the buffers of the control modules, for example, a combination of buffer data (0000) and (0100) surrounded by a circle with a horizontally extending dotted line in the copy source device 2301.

The information relating to the buffer set includes association information that associates each buffer data with a buffer in the copy target device 2302 that stores the buffer data. For example, the buffer data stored in the buffer with the buffer ID of 0000 is associated with a buffer with a buffer ID of 1000 that stores the buffer data, in the buffer set information storage unit in the control module #00.

In the above configuration, (a) the control modules #00 and #01 store Write data in storage media in response to a Write I/O command from a host computer or the like.

Simultaneously, (b) the control modules #00 and #01 transfer and store the Write data in the buffers. At this time, the Write data is managed on a buffer set-by-buffer set basis.

Then, (c) when writing the Write data in the buffers is completed, the control modules #00 and #01 start data transfer for the Write data, i.e., start remote copy on buffer set-by-buffer set basis.

(d) The write data sent from the copy source device 2301 by the remote copy is stored in the buffers included in the control modules #10 and #11 in the copy target device 2302 in accordance with the buffer set information. Then, the control modules #10 and #11 reflect the Write data stored in the buffers into the storage media.

When the above processing is completed, (e) the control modules in the copy source device 2301 and the copy target device 2302 release the buffers etc.

As described above, the buffer set is collectively controlled by performing the data transmission, collectively by using the write only buffer. Then in the copy target device 2302, the data is expanded in the storage media on buffer set-by-buffer set basis. Accordingly, the ordering is ensured.

Relating to the above technique, a storage device is known. If a failure occurs, the storage device immediately reflects dirty data to a disk device in accordance with the priority of data that is set in a logical device, and processes a job relating to important work with a high priority, thereby reducing degradation in host processing performance.

Also, a backup device is known. The backup device monitors use states of write buffers that temporarily store write data, writes out information in the buffers to a high-speed disk system if free spaces of the buffers become small, and writes back the information to the buffers if the use states of the buffers are improved.

Further, a computer system is known. The computer system prevents overflow of side files and cache files, and safely and efficiently performs remote copy between disk array devices.

Japanese Laid-open Patent Publication Nos. 2005-149436, 2006-268420, and 2007-140651 are examples of related art.

Referring to FIG. 24, in the copy source device 2301, however, the buffers that store the transferred Write data, and the BIT storage unit are not released and held until the Write data is expanded into the storage media in the copy target device 2302.

Thus, (f) in a case in which the processing for expanding the Write data into the storage media is delayed in the copy target device 2302, if line performance between the copy source device 2301 and the copy target device 2302 is low or unstable, the transfer processing may be delayed.

For example, if the transfer processing is delayed because a line bandwidth between the copy source device 2301 and the copy target device 2302 is low or unstable, the time of using the buffers and the BIT storage units in the copy source device 2301 and the copy target device 2302 may increase due to the delay. Thus, the memory cannot be released during that time.

(g) In this state, the copy source device 2301 stores Write data every time when the copy source device 2301 receives a new Write I/O command from the host computer or the like. Consequently, the buffers in the copy source device 2301 are consumed one after another.

(h) If this state continues, the buffers capable of storing the Write data may be insufficient, and shortage of a buffer in the copy source device 2301 may occur. Also, if the Write data has a size equivalent to or larger than the assigned buffer, the shortage of a buffer may occur.

In the state in which the buffer is used up, the copy source device 2301 stops without processing the Write I/O command from the host computer or the like. This state cannot be continued for a long time.

Hence, (i) the processing of the Write I/O command is temporarily stopped, and if the state in which the buffer is used up is not settled although a predetermined time elapses, buffer Halt processing is performed. The copy source device 2301 and the copy target device 2302 perform the buffer Halt processing, to clear the buffer and resume the processing of the Write I/O command.

At this time, the copy source device 2301 writes back the information of the Write data etc. in the buffer into a dedicated bit map. The copy source device 2301 performs remote copy transfer that does not ensure the ordering, in accordance with the bit map after the buffer Halt processing is executed. In this case, the remote copy that ensures the ordering may be suspended.

SUMMARY

According to an aspect of the invention, a storage apparatus connected to a storage device includes a storage module, a memory for storing data to be copied to the storage device, a plurality of save buffers for temporarily saving the data stored in the memory, the data saved in one of the plurality of save buffers being capable of being rebuilt on the basis of the saved data stored in the rest of the save buffers, and a control module for executing receiving a write request including the data to be stored in the storage apparatus from an external device, storing the data included in the write request to the storage module, storing the data included in the write request to the memory, copying the data stored in the memory to the storage device, saving the data stored in the memory to the save buffer when a rate of use of the memory which stores the data of the copying is greater than a predetermined rate, writing the saved data stored in the save buffer to the memory when a rate of use of the memory which stores the data of the copying is not greater than the predetermined rate, detecting a failure of the one of the plurality of save buffers, and rebuilding the saved data stored in the one of the plurality of save buffers on the basis of state information indicating a state of the plurality of save buffers.

The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 briefly illustrates a configuration of a storage system.

FIG. 2 illustrates an exemplary specific configuration of a memory included in a control module.

FIG. 3 illustrates an exemplary configuration of a buffer management table.

FIG. 4 illustrates an exemplary configuration of a buffer set management table.

FIG. 5 illustrates an exemplary configuration of a save buffer management table.

FIG. 6 illustrates an exemplary configuration of a save buffer.

FIG. 7 illustrates an exemplary configuration of a save buffer.

FIG. 8 is an illustration explaining the save buffer.

FIG. 9 is an illustration explaining buffer save processing.

FIG. 10 is an illustration explaining buffer save processing.

FIG. 11A is a flowchart briefly illustrating remote copy.

FIG. 11B is a flowchart briefly illustrating remote copy.

FIG. 12 is a flowchart illustrating processing for generating a region of the save buffer.

FIG. 13 is a flowchart illustrating specific processing for assigning the save buffer to control modules.

FIG. 14 is an illustration explaining write back pointer information and stage pointer information in the buffer save processing.

FIG. 15 is a flowchart illustrating update processing for the write back pointer information.

FIG. 16 is a flowchart illustrating update processing for the stage pointer information.

FIG. 17 is a flowchart illustrating writing back.

FIG. 18 illustrates a specific example of writing back.

FIG. 19 illustrates a specific example of writing back.

FIG. 20A is a flowchart illustrating staging.

FIG. 20B is a flowchart illustrating staging.

FIG. 21 is a flowchart illustrating rebuild processing for the save buffer.

FIG. 22 is a flowchart illustrating specific processing of matching processing illustrated in FIG. 11B.

FIG. 23 is an illustration explaining a RAID device having a remote copy function that ensures ordering.

FIG. 24 is an illustration explaining a RAID device having a remote copy function that ensures ordering.

DESCRIPTION OF EMBODIMENTS

Examples of these embodiments will be described below with reference to FIGS. 1 to 22.

FIG. 1 briefly illustrates a configuration of a storage system 100 according to this embodiment.

The storage system 100 illustrated in FIG. 1 includes a RAID device 110 and a RAID device 120 connected to the RAID device 110 through a network or a dedicated line 130 such that communication is allowed therebetween.

The RAID device (storage apparatus) 110 is a RAID device of distributed cache memory type that includes control modules #00 to #03 that have memories used for cache memories etc., a disk device 117 having a storage device such as a magnetic disk device, and a save buffer 118.

The control modules #00 to #03 are connected with the disk device 117 and the save buffer 118. The save buffer 118 includes a standby disk device 119; however, FIG. 1 illustrates these component separately for clarification. The save buffer 118 and the standby disk device 119 may be individual devices.

The control module #00 includes a central processing unit (CPU) 111 a, a memory 112 a, a channel adapter (CA) 113 a, a remote adapter (RA) 114 a, and fibre channels (FCs) 115 a and 116 a.

The CPU 111 a executes a predetermined program command, causes the control module #00 to operate, and hence actualizes remote copy that ensures ordering according to this embodiment.

The memory 112 a is used not only for the cache memory but also for a write only buffer 201 and a buffer set information storage unit 202 (described later).

The CA 113 a is an interface control unit for a host 150 that is a host computer connected with the RAID device 110. The RA 114 a is an interface control unit for another RAID device connected therewith through the network or the dedicated line 130.

The FCs 115 a and 116 a are interface control units for the disk device 117 and the save buffer 118. In this embodiment, the FC 115 a is connected with the disk device 117, and the FC 116 a is connected with the save buffer 118.

The other control modules #01 to #03 in the RAID device 110 and control modules #00 to #03 in the RAID device 120 have configurations similar to the control module #00 in the RAID device 110. However, the RAID device 120 (serving as a copy target device, described later) does not have to include a save buffer.

In the above configuration, for example, “data group output means,” “save and storage processing means,” and “rebuild control means” may be actualized if the CPU 111 a executes program commands expanded in a predetermined region in the memory 112 a.

A “data group” may be actualized by using buffer set data.

“Data group storage means” may be actualized by using part of or the entire save buffer 118. Alternatively, the “data group storage means” may be actualized by using part of the disk device 117.

“First storage means” may be actualized by using a partial region of the memory 112 a.

The RAID devices 110 and 120 each have the four control modules #00 to #03 in FIG. 1. However, it is not limited thereto. The RAID devices 110 and 120 are only required to be RAID devices of distributed cache memory type. The numbers of the CPUs, CAs, RAs, and FCs are not limited to those numbers illustrated in FIG. 1.

In the following embodiment, a case will be described in which remote copy is performed from the RAID device 110 to the RAID device 120. In this case, the RAID device 110 is called “copy source device 110,” and the RAID device 120 is called “copy target device 120.”

FIG. 2 illustrates an exemplary specific configuration of a memory 200 included in a control module according to this embodiment, more specifically, the memory 112 a included in the control module #00 in the RAID device 110 illustrated in FIG. 1.

Memories 112 b, 112 c, and 112 d in the control modules #01 to #03 in the RAID device 110 and memories 122 a, 122 b, 122 c, and 122 d included in the control modules #00 to #03 in the RAID device 120 may have a configuration similar to that illustrated in FIG. 2.

The memory 200 illustrated in FIG. 2 includes a write only buffer 201 and a buffer set information storage unit 202. The memory 200 also includes a buffer management table storage unit 203, a buffer set management table storage unit 204, a save buffer management table storage unit 205, and an unused buffer ID storage unit 206.

The write only buffer 201 includes a buffer 201 a and a BIT storage unit 201 b.

The buffer 201 a temporarily stores data to be stored in the disk device 117 or data stored in the disk device 117 such as Write data (described later). The buffer 201 a according to this embodiment is divided into 8 regions each having a given size. Specific identification information is assigned to each of the divided regions. The buffer 201 a is divided into the 8 regions in this embodiment; however, the configuration is not limited to that the buffer 201 a is divided into the 8 regions.

Hereinafter, the divided regions are called “individual buffers.” The identification information assigned to each individual buffer is called “buffer ID.” Data stored in an individual buffer indicated by a certain buffer ID is called “buffer data.”

For example, regarding (0000), (0001), (0002) . . . written in the buffer 201 a in FIG. 2, the numbers 0000, 0001, 0002 . . . provided in parentheses are buffer IDs respectively assigned to the individual buffers. The parenthetical numbers (0000), (0001), (0002) . . . are buffer data stored in the individual buffers indicated by the buffer IDs provided in parentheses.

The BIT storage unit 201 b stores a BIT including a logical unit (LU) where buffer data stored in the individual buffer in the buffer 201 a is expanded, a logical block address (LBA), a data size, the number of copy sessions, etc.

The numbers 0000, 0001, 0002 . . . written in the BIT storage unit 201 b represent the buffer IDs assigned to the individual buffers in the buffer 201 a. For example, the number 0000 in the BIT storage unit 201 b stores a BIT including a LU where buffer data stored in the individual buffer with the buffer ID of 0000 is expanded, a LBA, a data size, the number of copy sessions, etc.

The buffer set information storage unit 202 stores identification information indicative of a combination of individual buffers to be used next in control modules in a single RAID device. That is, the buffer set information storage unit 202 stores a buffer set ID (described later).

Hereinafter, a combination of individual buffers in control modules in a single RAID device is called “buffer set.” Identification information assigned to a buffer set is called “buffer set ID.” Information relating to a buffer set is called “buffer set information.” Buffer data stored in a buffer set is collectively called “buffer set data.”

In this embodiment, the buffer 201 a in each control module includes the 8 individual buffers, and hence the number of buffer sets is also 8. To simplify the description, it is assumed that a buffer set ID is equivalent to a buffer ID of an individual buffer in a master control module (described later).

The buffer set information also includes information that associates an individual buffer in a control module in the copy source device 110 with an individual buffer in a control module in the copy target device 120 when remote copy is performed between the RAID devices. Processing for adding the association information to the buffer set information is called “matching processing.”

Hereinafter, a buffer ID of an individual buffer in a control module in the copy source device 110 is called “copy source ID.” A buffer ID of an individual buffer in a control module in the copy target device 120 is called “copy target ID.”

For example, since the RAID device 110 is the RAID device of distributed cache memory type, data such as Write data is stored in individual buffers in each module, or particularly in an example illustrated in FIG. 2, data is distributed into individual buffers with buffer IDs of 0000, 0100, 0200, and 0300.

In this case, the buffer set information storage unit 202 stores buffer set information indicative of a buffer set including the individual buffers with the buffer IDs of 0000, 0100, 0200, and 0300.

The buffer set information includes combination information indicative of combinations of copy source IDs and copy target IDs, such as 0000 and 1000, 0100 and 1100, 0200 and 1200, and 0300 and 1300.

It is assumed that the buffer IDs 0000, 0100, 0200, and 0300 stored in the buffer set information storage unit 202 illustrated in FIG. 2 indicate individual buffers respectively included in the control modules #00, #01, #02, and #03 in the copy source device 110.

Also, it is assumed that buffer IDs 1000, 1100, 1200, and 1300 stored in the buffer set information storage unit 202 illustrated in FIG. 2 indicate individual buffers respectively included in the control modules #00, #01, #02, and #03 in the copy target device 120.

Remote copy according to this embodiment is performed on a buffer set-by-buffer set basis. Copy subject data in each buffer set includes a BIT and buffer data stored in the write only buffer 201, and buffer set information stored in the buffer set information storage unit 202.

In this embodiment, the copy subject data in each buffer set is managed as a single “generation.” A specific example of the generation is illustrated in FIG. 8.

The buffer management table storage unit 203 stores a buffer management table 300 used for management of, for example, the write only buffer 201. The buffer management table 300 will be described later.

The buffer set management table storage unit 204 stores a buffer set management table 400 used for management of use states of buffer sets. The buffer set management table 400 will be described later.

The save buffer management table storage unit 205 stores a save buffer management table 500 used for management of the save buffer 118. The save buffer management table will be described later.

The unused buffer ID storage unit 206 stores buffer IDs of unused individual buffers in the copy target device 120. Hereinafter, a buffer ID of an unused individual buffer is called “unused buffer ID.” For example, when the copy source device 110 receives notification of an unused buffer ID from the copy target device 120, the copy source device 110 stores the notified unused buffer ID in the unused buffer ID storage unit 206.

With the above configuration, in the remote copy according to this embodiment, the copy source device 110 collectively performs processing for storing Write data in the write only buffer 201 and processing for transferring the Write data to the copy target device 120 on a buffer set-by-buffer set basis.

Similarly, in the remote copy according to this embodiment, the copy target device 120 collectively performs processing for expanding the Write data transferred from the copy source device 110 into a disk device 127 on a buffer set-by-buffer set basis. Consequently, the remote copy that ensures ordering is actualized.

The remote copy that ensures the ordering by using the buffer set is a known technique. For example, Japanese Laid-open Patent Publication No. 2006-260292 discloses the technique.

FIG. 3 briefly illustrates an exemplary configuration of the buffer management table 300 according to this embodiment.

The buffer management table 300 includes a subject buffer set ID, write back pointer information, and stage pointer information.

The subject buffer set ID is information indicative of a buffer set ID of a buffer set that is currently used. The write back pointer information is information indicative of a generation subjected to writing back (described later). The stage pointer information is information indicative of a generation that staging is performed last.

FIG. 4 briefly illustrates an exemplary configuration of the buffer set management table 400 according to this embodiment.

The buffer set management table 400 includes a buffer set ID, a purpose of use, a subject generation, and a stored number of I/O.

The purpose of use is previously set for each buffer set indicated by a buffer set ID. For example, when the buffer set is used for staging, “staging” is set. Similarly, when the buffer set is used for writing back, “writing back” is set. If the buffer set merely stores copy data of Write data, “storing” is set.

The subject generation is a generation subjected to processing that is set in accordance with the purpose of use. The stored number of I/O is a number of I/O stored in a buffer set. The subject generation and the stored number of I/O are, for example, updated by the copy source device 110 every time when Write data is stored in a buffer set.

The character “-” in FIG. 4 represents an example in which an “unused state” is set.

FIG. 5 briefly illustrates an exemplary configuration of the save buffer management table 500 according to this embodiment.

The save buffer management table 500 includes the maximum number of generations for copy subject data that can be stored in the save buffer 118, and a save position defining a leading address of a storage region that is a storage region in the save buffer 118 and is assigned to each control module.

The maximum number of generations is determined, for example, when the save buffer 118 is initialized.

Hereinafter, a storage region for a single generation that is in the save buffer 118 and assigned to each control module is called “individual save buffer.” For example, three divided regions in LU#0 in FIG. 6 are individual save buffers.

FIGS. 6 and 7 briefly illustrate exemplary configurations of the save buffer 118 according to this embodiment. Referring to FIGS. 6 and 7, the control modules #00 to #03 are schematically illustrated in a simple manner such that only the buffers 201 a in the write only buffers 201 are illustrated. However, the configurations of the control modules #00 to #03 are not limited thereto. Also, a dotted line extending over the control modules #00 to #03 indicates a buffer set for a single generation.

FIG. 6 illustrates an example configuration in a case in which the save buffer 118 is configured by a single RAID group.

A RAID group 600 illustrated in FIG. 6 and used for the save buffer 118 includes logical units LU#0 to LU#F. Groups of logical units surrounded by horizontally extending dotted lines, i.e., LU#0 to LU#3, LU#4 to LU#7, LU#8 to LU#B, and LU#C to LU#F respectively configure volume groups.

The RAID group 600 is used on a volume group-by-volume group basis. Volume groups are assigned to the write only buffers in the control modules.

For example, regarding the RAID group 600 illustrated in FIG. 6, the logical units LU#0, LU#4, LU#8, and LU#C are assigned to the write only buffer in the control module #00. The logical units LU#1, LU#5, LU#9, and LU#D are assigned to the write only buffer in the control module #01.

The logical units LU#2, LU#6, LU#A, and LU#E are assigned to the write only buffer in the control module #02. The logical units LU#3, LU#7, LU#B, and LU#F are assigned to the write only buffer in the control module #03.

If the number of logical units of a volume group is larger than the number of control modules, a plurality of logical units may be assigned to a single control module. Also, referring to FIG. 8, a logical unit of a volume group is divided into regions each having a size including an individual buffer that stores buffer data, a BIT, and buffer set information. The divided region is the above-mentioned “individual save buffer.”

For example, buffer data stored in the individual buffers in the control modules is stored in the individual save buffers in a volume group assigned to the control modules, in order of the generation of the individual save buffers as indicated by an arrow in FIG. 6.

FIG. 7 illustrates an example configuration in a case in which the save buffer 118 according to this embodiment is configured by two RAID groups.

A RAID group 700 used for the save buffer 118 illustrated in FIG. 7 includes a RAID group 701 including logical units LU#0 to LU#F, and a RAID group 702 including logical units LU#10 to LU#1F.

In the RAID group 701, LU#0 and LU#2 configure a volume group. Also, LU#1 and LU#3, LU#4 and LU#6, LU#5 and LU#7, LU#8 and LU#A, LU#9 and LU#B, LU#C and LU#E, and LU#D and LU#F respectively configure volume groups.

In the RAID group 702, LU#10 and LU#12 configure a volume group. Also, LU#11 and LU#13, LU#14 and LU#16, LU#15 and LU#17, LU#18 and LU#1A, LU#19 and LU#1B, LU#1C and LU#1E, and LU#1D and LU#1F respectively configure volume groups.

Logical units in a volume group of the RAID group 700 are assigned to the write only buffers in the control modules.

For example, regarding the RAID group 700 illustrated in FIG. 7, the logical units LU#0, LU#1, LU#4, LU#5, LU#8, LU#9, LU#C, and LU#D are assigned to the write only buffer in the control module #00. The logical units LU#2, LU#3, LU#6, LU#7, LU#A, LU#B, LU#E, and LU#F are assigned to the write only buffer in the control module #01.

The logical units LU#10, LU#11, LU#14, LU#15, LU#18, LU#19, LU#1C, and LU#1D are assigned to the write only buffer in the control module #02. The logical units LU#12, LU#13, LU#16, LU#17, LU#1A, LU#1B, LU#1E, and LU#1F are assigned to the write only buffer in the control module #03.

A logical unit of a volume group is divided into regions each having the same size as that of an individual buffer. For example, buffer data stored in an individual buffer in a control module is stored in an individual save buffer of a volume group assigned to the control module, in order of the generation of an individual save buffer as indicated by an arrow in FIG. 7.

Referring to FIG. 7, if the write only buffers in the control modules are assigned to at least two RAID groups, a load of each RAID group can be distributed. FIG. 7 illustrates the case in which the two RAID groups are used; however, a similar advantage can be attained even if more than two RAID groups are used.

As described above, the save buffer 118 according to this embodiment, for example, LU#0 to LU#F illustrated in FIG. 6, or LU#0 to LU#F and LU#10 to LU#1F illustrated in FIG. 7 each are divided into individual save buffers each having a size including an individual buffer, a BIT, and buffer set information and used. FIG. 8 illustrates the overview. In each individual save buffer of the save buffer 118, copy subject data (data to be copied), which particularly includes buffer set information, a BIT, and buffer data, is stored in order of the generation.

FIGS. 9 and 10 are illustrations each explaining buffer save processing.

For easier understanding, the configuration of the copy source device 110 is only briefly illustrated. For example, only the control modules #00 and #01 are illustrated; however, the configuration of the copy source device 110 is not limited to those illustrated in FIGS. 9 and 10. Also, the control modules respectively include disk devices 117 for the convenience of description. However, the configuration of the copy source device 110 is not limited to those illustrated in FIGS. 9 and 10.

FIG. 9 is an illustration explaining buffer save processing upon reception of a Write I/O command while buffer sets 1 to 4 are in use because data in the buffer sets is during the transferring or waiting for the expansion processing by the copy target device 120. Hereinafter, all control modules included in the copy source device 110 are collectively called a “control module.”

(a) Upon the reception of the Write I/O command, the control module stores Write data in the disk device 117 in the control module, and (b) stores copy data of the Write data in a buffer set 5. Hereinafter, the copy data of the Write data in this case is called “Write data.”

For example, if the rate of use of buffer sets becomes a certain level or higher, (c) the control module saves to the save buffer 118 the buffer set data of the generation 5, which is stored in the buffer set 5 and expected to be transferred to the copy target device 120 next. Simultaneously, the control modules change the storage target for new Write data or the like from the buffer set 5 to a buffer set 6.

Herein, the rate of use of buffer sets may be a value that is obtained by “number of buffer sets in use”/“total number of buffer sets.” The wording “in use” means, for example, a state during transferring to the copy target device 120 or during waiting for release. The control module according to this embodiment saves to the save buffer 118 the buffer data in the buffer set, which is expected to be transferred to the copy target device 120 next, if the rate of use of the buffer sets reaches 50% or higher.

For example, if it is detected that the disk device that configures the save buffer 118 is not available due to a failure or the like, (c′) the control module performs rebuild processing to maintain the redundant configuration of the save buffer 118.

Rebuild processing includes changing a failed disk device into a new disk device, the failed disk device being one of the disk devices included in the save buffer 118, rebuilding the data stored in the failed disk device by using the data stored in the rest of the disk devices included in the save buffer 118, and writing the rebuilt data into the new disk device. In this embodiment, the rebuilding process which is executed by the RAID device includes rebuilding the data stored in the failed disk device by using the data stored in the rest of the disk devices included in the save buffer 118, and writing the rebuilt data into the new disk device.

At this time, the control module executes the rebuild processing by taking into account the use state and the I/O load of the buffer set.

(d) Upon reception of new Write I/O command, the control module stores Write data in the disk device, and stores copy data of the Write data in the changed buffer set 6. The buffer set data stored in the buffer set 6 corresponds to a generation 6.

At this time, since the elder generation than the generation 6 for the buffer set 6, for example, the generation 5 in FIG. 10 is saved to the save buffer 118, (e) the control module saves the buffer set data stored in the buffer set 6, to the save buffer 118.

If the buffer set 1 in use is released, (f) the control module reads out the buffer set data of the generation 5 stored in the save buffer 118, and stores the buffer set data in the buffer set 1. In this embodiment, “releasing” means bringing a buffer set into an unused state.

When the rebuild processing is executed, (f′) the control module executes the rebuild processing by taking into account the use state and the I/O load of a buffer set.

FIGS. 11A and 11B are flowcharts briefly illustrating the remote copy according to this embodiment. The remote copy according to this embodiment will be briefly described below with reference to FIGS. 11A and 11B.

When the copy source device 110 starts up, the copy source device 110 performs buffer initial configuration processing. For example, the copy source device 110 secures the regions for the configuration illustrated in FIG. 2 in the memory 200 included in each control module in accordance with predetermined configuration information, and initializes the regions.

The copy source device 110 assigns volume groups to the write only buffers in the control modules. Specific processing will be described with reference to FIGS. 12 and 13.

The copy source device 110 generates buffer sets, and performs initial generation processing for the generated buffer sets. For example, the copy source device 110 generates buffer sets by combining individual buffers of the control modules. The copy source device 110 stores the generated buffer sets as buffer set information in the buffer set information storage unit 202.

The copy target device 120 also performs the above processing.

The copy source device 110 initializes the buffer management table 300, the buffer set management table 400, and the save buffer management table 500.

With the above processing, preparation for the remote copy from the copy source device 110 to the copy target device 120 is completed. When the preparation for receiving the Write I/O command from the host 150 is completed, the remote copy is started (S1100 a, S1100 b).

In S1101 a, the copy source device 110 issues an unused buffer notification request command to the copy target device 120 so as to request notification of an unused individual buffer.

Meanwhile, the copy target device 120 shifts the processing to S1101 b, and monitors the unused buffer request command until the copy target device 120 receives the unused buffer notification request command from the copy source device 110 (S1101 b, NO).

In S1101 b, if the copy target device 120 detects the unused buffer notification request command from the copy source device 110 (S1101 b, YES), the copy target device 120 shifts the processing to S1102 b.

In S1102 b, the copy target device 120 retrieves an individual buffer whose region is released and unused. If the copy target device 120 detects an individual buffer whose region is released and unused, the copy target device 120 notifies a buffer ID of the detected individual buffer as an unused buffer ID to the copy source device 110.

Meanwhile, when the copy source device 110 receives the notification of the unused buffer ID from the copy target device 120, the copy source device 110 stores the notified unused buffer ID in the unused buffer ID storage unit 206.

In S1102 a, the copy source device 110 acquires a subject buffer set that stores Write data. The subject buffer set that stores the Write data is called “storage subject buffer set.”

For example, the copy source device 110 refers to the buffer set management table 400, and acquires a buffer set ID in an unused state. Then, the copy source device 110 sets the acquired buffer set ID as a subject buffer set ID in the buffer management table 300.

The copy source device 110 determines a buffer set with a buffer set ID that is set as the subject buffer set ID in the buffer management table 300, as the “storage subject buffer set,” and performs processing as follows.

The copy source device 110 does not perform matching processing in S1102 a. The copy source device 110 performs the matching processing in S1111 a (described later), that is, before transmission processing for buffer set data.

In S1103 a, the copy source device 110 updates the generation set in the write back pointer information in the buffer management table 300 to a value incremented by 1.

In S1104 a, the copy source device 110 performs processing for storing the Write data in individual buffers of the storage subject buffer set.

For example, it is assumed that the copy source device 110 receives the Write I/O command from the host 150. Then, the copy source device 110 stores the Write data received with the Write I/O command in the storage subject buffer set indicated by the subject buffer set ID currently used in the buffer management table 300, or particularly stores the Write data in individual buffers of the control modules in a distributed manner.

In S1105 a, the copy source device 110 judges whether a storage region that stores the data remains in the storage subject buffer set. If no storage region remains (S1105 a, NO), the copy source device 110 shifts the processing to S1107 a.

In S1105 a, if the storage region remains (S1105 a, YES), the copy source device 110 shifts the processing to S1106 a. In this case, the copy source device 110 judges whether a predetermined time has elapsed after the acquisition of the storage subject buffer set (S1106 a).

If the predetermined time has not elapsed (S1106 a, NO), the copy source device 110 shifts the processing to S1104 a. If the predetermined time has elapsed (S1106 a, YES), the copy source device 110 shifts the processing to S1107 a.

In S1107 a, the copy source device 110 acquires new storage subject buffer set by processing similar to S1102 a. In S1108 a, the copy source device 110 changes the storage subject buffer set to the new storage subject buffer set acquired in S1107 a.

The storage subject buffer set before the change is called “write-back subject buffer set” in the processing in S1110 a, and is called “transfer subject buffer set” in the processing in S1111 a or later.

In S1109 a, the copy source device 110 updates the write back pointer information by processing similar to S1103 a.

In S1110 a, the copy source device 110 performs write back processing. When the staging is completed, the copy source device 110 shifts the processing to S1111 a.

In S1111 a, the copy source device 110 performs the matching processing. For example, the copy source device 110 acquires an unused buffer ID from the unused buffer ID storage unit 206. The copy source device 110 assigns the acquired unused buffer ID to a copy target ID of the transfer subject buffer set, to associate a copy source ID of the transfer subject buffer set with the copy target ID.

In S1112 a, the copy source device 110 transmits buffer set data stored in the transfer subject buffer set to the copy target device 120. The buffer set data includes buffer data stored in the buffer 201 a, a BIT stored in the BIT storage unit 201 b, and buffer set information stored in the buffer set information storage unit 202 in each control module.

Meanwhile, when the copy target device 120 receives the buffer set data from the copy source device 110, the copy target device 120 shifts the processing to S1103 b.

In S1103 b, the copy target device 120 performs reception processing for the buffer set data. For example, the copy target device 120 stores the buffer data in the buffer 201 a, the BIT in the BIT storage unit 201 b, and the buffer set information in the buffer set information storage unit 202, from among the received buffer set data.

In S1104 b, the copy target device 120 judges whether the copy target device 120 has received all buffer set data. If the copy target device 120 has received not all buffer set data (S1104 b, NO), the copy target device 120 shifts the processing to S1103 b, and repeats the processing from S1103 b to S1104 b.

In S1104 b, if the copy target device 120 has received all buffer set data (S1104 b, YES), the copy target device 120 shifts the processing to S1105 b.

In S1105 b, the copy target device 120 determines whether the buffer set data acquired in S1103 b can be expanded in the disk device 127 that is a storage device included in the copy target device 120. If the data can be expanded (S1105 b, YES), the copy target device 120 shifts the processing to S1106 b.

In S1106 b, the copy target device 120 expands the buffer set data acquired in S1103 b, in the disk device 127 included in the copy target device 120. When the expansion is ended, the copy target device 120 shifts the processing to S1107 b, and notifies the completion of the expansion of the buffer set data to the copy source device 110. Hereinafter, the notification is called “buffer set data expansion completion notification.”

When the expansion of the buffer set data in the disk device 127 is ended, in S1108 b, the copy target device 120 performs buffer set release processing. For example, the copy target device 120 sets the buffer set, whose buffer set data has been expanded in the disk device 127, to be an unused state.

In S1109 b, the copy target device 120 uses the released region and secures new regions in the buffer set information storage unit 202 and the write only buffer 201, so as to construct the configuration illustrated in FIG. 2.

When the above processing is ended, the copy target device 120 shifts the processing to S1110 b, and notifies an unused buffer ID that newly becomes available as a result of the processing in S1108 b to S1109 b to the copy source device 110 (S1110 b). When the copy source device 110 receives the unused buffer ID, the copy source device 110 stores the notified unused buffer ID in the unused buffer ID storage unit 206.

Meanwhile, in S1113 a, the copy source device 110 determines whether the copy source device 110 has received the buffer set data expansion completion notification from the copy target device 120. If the copy source device 110 does not receive the buffer set data expansion completion notification (S1113 a, NO), the copy source device 110 repeats the processing in S1113 a. If the copy source device 110 has received the buffer set data expansion completion notification from the copy target device 120 (S1113 a, YES), the copy source device 110 shifts the processing to S1114 a.

In S1114 a, like S1108 b, the copy source device 110 performs the buffer set release processing for the transfer subject buffer set with the buffer set data transmission processing performed in S1112 a. In particular, the copy source device 110 refers to the buffer set management table 400, and sets the transfer subject buffer set, whose data has been transferred, to be an unused state.

In S1115 a, the copy source device 110 refers to the buffer management table 300, and updates the generation set in the stage pointer information to a value incremented by 1.

In S1116 a, the copy source device 110 performs buffer reconfiguration processing by, for example, initializing the region of the buffer set brought into an unused state.

In S1117 a, the copy source device 110 judges whether the staging is required. For example, the copy source device 110 judges the necessity of the staging by determining whether the save buffer 118 includes a saved generation.

The copy source device 110 can determine the presence of the saved generation in the save buffer 118 by the following processing (a) to (d).

(a) The copy source device 110 refers to the buffer management table 300, and acquires the write back pointer information and the stage pointer information.

(b) The copy source device 110 refers to the buffer set management table 400, and retrieves a generation not included in the buffer set management table 400 by successively checking generations in ascending order from the generation obtained by adding 1 to the generation corresponding to the stage pointer information.

For example, the buffer management table 300 illustrated in FIG. 3 includes a generation 2 for the stage pointer information. The copy source device 110 refers to the buffer set management table 400 illustrated in FIG. 4, and successively checks the generation 3, obtained by adding 1 to the generation 2, and then generations 4, 5, . . . , in ascending order. Thus, the copy source device 110 detects a generation 7 not included in the buffer set management table 400.

(c) The copy source device 110 refers to the buffer set management table 400, and retrieves a generation not included in the buffer set management table 400 by successively checking generations in descending order from the generation corresponding to the write back pointer information.

For example, the buffer management table 300 illustrated in FIG. 3 includes a generation 15 for the write back pointer information. The copy source device 110 refers to the buffer set management table 400 illustrated in FIG. 4, and successively checks the generations 15, 14, 13 . . . , in descending order. Thus, the copy source device 110 detects a generation 12 not included in the buffer set management table 400.

(d) With the above processing, it is found that the detected generations 7 to 12 are saved to the save buffer 118.

In S1117 a, if the save buffer 118 includes the saved generations (S1117 a, YES), the copy source device 110 shifts the processing to S1118 a. If the save buffer 118 includes no saved generation (S1117 a, NO), the copy source device 110 shifts the processing to S1120 a.

In S1118 a, the copy source device 110 acquires a buffer set used for the staging, i.e., a staging buffer set.

For example, the copy source device 110 refers to the buffer set management table 400, and acquires a buffer set ID in an unused state, as a “staging subject buffer set ID.”

The copy source device 110 refers to the buffer set management table 400, and sets a subject generation with a buffer set ID corresponding to the staging subject buffer set ID, to a staging subject generation (described later).

The copy source device 110 refers to the buffer set management table 400, and sets the purpose of use for the buffer set ID corresponding to the staging subject buffer set ID, to the “staging.”

In S1119 a, the copy source device 110 performs the staging. When the staging is completed, the copy source device 110 shifts the processing to S1111 a.

When the above processing is ended, the copy source device 110 ends the remote copy, or shifts the processing to S1104 a to continue the remote copy. When the copy source device 110 receives new Write I/O command from the host 150, the copy source device 110 shifts the processing to S1104 a etc., and continues the remote copy.

When the above processing is ended, the copy target device 120 ends the remote copy, or shifts the processing to S1103 b to continue the remote copy.

The following processing in the remote copy according to this embodiment will be more specifically described below.

(1) Processing for generating region of save buffer 118

(2) Processing for assigning save buffer 118 to control modules

(3) Processing for updating write back pointer information and stage pointer information

(4) Writing back from write only buffer 201 to save buffer 118

(5) Staging from save buffer 118 to write only buffer 201

(6) Rebuilding for save buffer 118

In this embodiment, storing data stored in the write only buffer 201 into the save buffer 118 is called “writing back,” and storing data stored in the save buffer 118 into the write only buffer 201 is called “staging.”

(1) Processing for Generating Region of Save Buffer 118

FIG. 12 is a flowchart illustrating the processing for generating the region of the save buffer 118 according to this embodiment. The processing illustrated in FIG. 12 may be executed during the maintenance operation of the copy source device 110.

In S1201, the copy source device 110 selects the region for the save buffer 118 from the buffer 201 a of the write only buffer 201. The copy source device 110 shifts the processing to S1202, and selects a disk device for configuring RAID in accordance with an input by a user.

In S1203, the copy source device 110 checks whether the disk device selected in S1202 satisfies a condition for configuring the RAID. If the disk device does not satisfy the condition (S1203, NO), the copy source device 110 displays a notice to ask the user to designate another disk device on a display device or the like, and shifts the processing to S1202.

In S1203, if the disk device satisfies the condition (S1203, YES), the copy source device 110 shifts the processing to S1204.

In S1204, the copy source device 110 generates a RAID group configured by the disk device selected in S1202, and reflects the information into configuration information that holds a device configuration etc. of the copy source device 110.

In S1205, the copy source device 110 generates a plurality of volumes in the RAID group generated in S1204. The copy source device 110 shifts the processing to S1206, and reflects the configuration of logical units generated in S1205 into the configuration information.

In S1207, the copy source device 110 determines volumes to be used in the control modules by the processing illustrated in FIG. 13 (hereinafter, the volumes are called “assigned volumes”). The control modules use the determined volumes as the region of the save buffer 118.

(2) Processing for Assigning Save Buffer 118 to Control Modules

FIG. 13 is a flowchart illustrating specific processing of assigning the save buffer 118 to the control modules according to this embodiment (S1207). The processing illustrated in FIG. 13 may be executed when the copy source device 110 starts up or during the maintenance operation.

In S1301, the copy source device 110 refers to the configuration information and acquires the number (A) of RAID groups assigned as the save buffer 118.

The copy source device 110 shifts the processing to S1302, and acquires the number (B) of control modules in the copy source device 110 from the configuration information.

In S1303, the copy source device 110 calculates the number (C) of control modules per RAID group by an expression (C)=(B)/(A). The copy source device 110 shifts the processing to S1304, and assigns control modules by the number (C) to each RAID group.

In S1305, the copy source device 110 divides the number of volumes in each RAID group by (C), and calculates the number (D) of assigned volumes. The copy source device 110 shifts the processing to S1306, and assigns the assigned volumes by the number (D) to each of the control modules assigned to the RAID group on the basis of the calculation result in S1305.

In S1307, the copy source device 110 reflects the configuration determined in the above processing into the configuration information and setting information included in each control module, and ends the processing (S1308).

(3) Processing for Updating Write Back Pointer Information and Stage Pointer Information

In the buffer save processing in this embodiment, a write position (generation) of data to be stored in the save buffer 118 and a read position (generation) of data to be read from the save buffer 118 are managed by using two pieces of information including the write back pointer information and the stage pointer information.

FIG. 14 is an illustration explaining the write back pointer information and the stage pointer information in the buffer save processing according to this embodiment. Reference sign 1401 in FIG. 14 indicates the save buffer 118 in a simple manner. Similarly, reference signs 1402 and 1403 in FIG. 14 indicate the buffer sets in a simple manner.

For example, a case is considered in which x-th time change for the buffer set is performed in the control module. In this case, the stage pointer information holds as information the generation that the staging has been performed last. The write back pointer information holds as information a generation x of the save buffer 1401.

Also, a case is considered in which buffer set data of the generation x is transferred to the copy target device 120 immediately after (x+1)-th time change for the buffer set is performed in the control module. In this case, when buffer set data stored in the generation x is staged and the transfer processing is completed, the stage pointer information is updated from the generation x to a generation x+1. The write back pointer information holds as the information the generation x+1 of the save buffer 1401.

Further, a case is considered in which buffer set data of the generation x+1 is written back to the save buffer 1401 when (x+2)-th time change for the buffer set is performed in the control module. In this case, if the generation of the save buffer 1401 held in the stage pointer information is the generation x, the next staging subject is the generation x+1. The write back pointer information holds the generation x+2 in the volume group.

As described above, every time when a buffer set is generated, the write back pointer information holds a next generation of that buffer set as information. Also, every time when the processing for the buffer set of the old generation after the change is completed, for example, every time when the transferring of buffer set data is completed in the copy source device 110 and the expansion of the data is completed in the copy target device 120, the stage pointer information is updated.

If there are a plurality of volume groups assigned as the save buffer 1401, the volume groups are used in ascending order of numbers assigned to the volume groups. If all volume groups are used up, the order returns to the first volume group, so that the volume groups are used cyclically.

FIGS. 15 and 16 explain specific update processing for the write back pointer information and the stage pointer information.

FIG. 15 is a flowchart illustrating the update processing for the write back pointer information according to this embodiment.

In S1500 a, a master control module that is representative of the control modules included in the copy source device 110 shifts the processing to S1501 a when the change processing for the buffer set is started.

In S1501 a, the master control module advances the currently holding write back pointer information by 1. For example, the currently held generation is incremented by 1 and is held as information for the next generation.

In S1502 a, the master control module updates the write back pointer information obtained in S1501 a by reflecting the buffer management table 300 of the master control module into the write back pointer information. The master control module requests the other control modules included in the copy source device 110 to perform processing similar to S1502 a.

Meanwhile, in S1501 b, each of the other control modules updates the write back pointer information obtained in S1501 a by reflecting buffer management table 300 of the control module into the write back pointer information. The control module notifies completion of the update of the buffer management table 300 to the master control module.

In S1503 a, the master control module checks whether the master control module has received replies from all requested control modules. If there is a control module without a reply (S1503 a, NO), the master control module repeats the processing in S1503 a.

In S1503 a, if the master control modules has received the replies from all requested control modules (S1503 a, YES), the master control module shifts the processing to S1504 a, and ends the update processing for the write back pointer information.

FIG. 16 is a flowchart illustrating the update processing for the stage pointer information according to this embodiment.

In S1600 a, the master control module in the copy source device 110 shifts the processing to S1601 a when the release processing for the buffer set is started.

In S1601 a, the master control module judges whether a release subject buffer set is present. If no release subject buffer set is present (S1601 a, NO), the master control module shifts the processing to S1604 a, and ends the processing.

In this embodiment, determined as the release subject buffer set is a buffer set notified such that the transferring of data in the buffer set to the copy target device 120 has been completed and that expansion of the transferred data into the disk device from the copy target device 120 has been completed.

In S1601 a, if the release subject buffer set is present (S1601 a, YES), the master control module shifts the processing to S1602 a.

In S1602 a, the master control module releases an individual buffer, a BIT, and buffer set information of the release subject buffer set, and updates the stage pointer information. The master control module requests the other control modules included in the copy source device 110 to perform processing similar to S1602 a.

In S1601 b, when each of the other control modules receives the request from the master control module, the control module releases the individual buffer, the BIT, and the buffer set information of the release subject buffer set, and updates the stage pointer information. When the processing is completed, the control module notifies the completion to the master control module.

In S1603 a, the master control module checks replies from the requested control modules, and judges whether the master control module has received the replies from all control modules. If there is a control module without a reply (S1603 a, NO), the master control module repeats the processing in S1603 a.

In S1603 a, if the master control module has received the replies from all requested control modules (S1603 a, YES), the master control module shifts the processing to S1604 a, and ends the update processing for the stage pointer information.

(4) Writing Back from Write Only Buffer 201 to Save Buffer 118

FIG. 17 is a flowchart illustrating the writing back according to this embodiment.

In S1700 a, for example, if the storage processing of the Write data in the buffer set is completed, the master control module in the copy source device 110 shifts the processing to S1701 a.

In S1701 a, the master control module acquires the number of buffer sets used for the staging or transferring. Hereinafter, the number of buffer sets that are in use during the staging or transferring is called the “number of buffer sets in use.” The master control module compares the number of buffer sets in use with a predetermined threshold, for example, a value that is 50% the total number of buffer sets. If the number of buffer sets in use is smaller than the threshold (S1701 a, NO), the master control module shifts the processing to S1710 a. If the number of buffer sets in use is the threshold or larger (S1701 a, YES), the master control module shifts the processing to S1702 a.

In S1702 a, the master control module judges whether rebuilding is in operation for the save buffer 118. If the rebuilding is in operation for the save buffer 118 (S1702 a, YES), the master control module shifts the processing to S1703 a.

To judge whether the rebuilding is in operation for the save buffer 118, a flag for a disk access stop mode (described later) may be used in this embodiment. In this case, the master control module may turn ON the flag for the disk access stop mode when the rebuilding is started, and the master control module may turn OFF when the rebuilding is ended.

In S1703 a, the master control module suspends the writing back. The master control module shifts the processing to S1704 a. In S1704 a, the master control module waits for completion of the rebuilding (including the end and suspension of the rebuilding). Then, if the completion of the rebuilding is detected by interruption or the like, the master control module starts the processing from S1705 a.

In S1702 a, if the rebuilding is not in operation (S1702 a, NO), the master control module shifts the processing to S1705 a.

In S1705 a, the master control module sets a rebuild stop mode. In this embodiment, a flag for the rebuild stop mode may be turned ON. Though described later, the master control module refers to the flag for the rebuild stop mode every time when the save buffer 118 is brought into the rebuilding. If the flag for the rebuild stop mode is ON, the master control module suspends the rebuilding.

The flag for the rebuild stop mode may be stored in, for example, a predetermined region in the memory 200 included in the master control module.

In S1706 a, the master control module performs the write back processing as follows. Herein, a buffer set subjected to the writing back is called “writing back subject generation.”

The master control module calculates an address of an individual save buffer, in which a writing back subject generation is stored, from the save buffer management table 500. The master control module stores in the calculated address buffer data, a BIT, and buffer set information stored in an individual buffer included in the master control module, from among the writing back subject buffer set described with reference to S1108 a in FIG. 11A. The processing is performed by each control module in the copy source device 110 as illustrated in FIGS. 6 and 7.

If the save buffer assigned to the control module has a continuous address space, a leading address of the individual save buffer can be obtained by adding “(writing back subject generation−1)×individual save buffer size” to “leading address of save data” set in the save buffer management table 500.

When the writing back is completed, the master control module requests the other control modules included in the copy source device 110 to perform processing similar to S1706 a.

In S1701 b, each of the other control modules acquires the buffer data, the BIT, and the buffer set information stored in the individual buffer included in the control module, from among the buffer set requested from the master control module, from the BIT storage unit 201 b etc. of the control module. The control module saves the acquired BIT and the buffer set information to an individual save buffer assigned to the control module.

If the save buffer assigned to each of the other control modules has a continuous address space, a leading address of the individual save buffer assigned to the control module can be obtained by adding “(writing back subject generation−1)×individual save buffer size” to “leading address of save data” set in the save buffer management table 500.

In S1702 b, each of the other control modules checks whether buffer data such as Write data is stored in the individual buffer included in the control module, from among the buffer set requested by the master control module.

If the buffer data such as the Write data is not preset in the individual buffer (S1702 b, NO), each of the other control modules skips S1703 b. If the buffer data such as the Write data is preset in the individual buffer (S1702 b, YES), the control module shifts the processing to S1703 b.

In S1703 b, each of the other control modules saves the buffer data such as the Write data stored in the individual buffer to the individual save buffer of the save buffer 118 assigned to the control module. Then, the control module notifies completion of the requested processing to the master control module.

Meanwhile, in S1707 a, the master control module checks whether the master control module has received replies from all requested control modules. If there is a control module without a reply (S1707 a, NO), the master control module repeats the processing in S1707 a.

If the master control module has received the replies from all control modules (S1707 a, YES), the master control module releases buffer set information etc. of the writing back subject buffer set (S1708 a). The master control module refers to the buffer set management table 400, and sets a buffer set ID corresponding to a buffer set ID of the writing back subject buffer set to an unused state.

In S1709 a, the master control module deactivates the rebuild stop mode. In particular, the master control module may turn OFF the flag for the rebuild stop mode.

In S1710 a, the master control module judges whether there is a rebuild queue for the save buffer 118. If there is the rebuild queue for the save buffer 118 (S1710 a, YES), the master control module shifts the processing to S1711 a. The master control module executes the rebuild processing. If the rebuild processing is completed, the master control module shifts the processing to, for example, S1712 a.

In S1710 a, if there is no rebuild queue for the save buffer 118 (S1710 a, NO), the master control module shifts the processing to S1712 a.

The rebuild processing for the save buffer 118 may be managed by using, for example, a hold queue. As long as the master control module refers to the hold queue, the master control module can recognize the presence of the rebuild queue for the save buffer 118.

When the above processing is ended, the master control module and the other control modules end the buffer save processing (S1712 a).

FIGS. 18 and 19 briefly illustrate specific examples of the writing back according to this embodiment. Reference sign 1801 in FIGS. 18 and 19 indicates the save buffer 118 in a simple manner. Reference signs 1802 to 1804 in FIGS. 18 and 19 indicate the buffer sets in a simple manner.

FIGS. 18 and 19 are illustrations explaining the writing back if the threshold described in FIG. 17 is the value that is 50% the total number of buffer sets when the copy source device 110 includes control modules #00 to #03, and each control module has 8 individual buffers.

A case is considered (a) in which buffer sets 1 to 4 are during transferring, waiting for completion of transferring, or waiting for releasing, and (b) in which a buffer set 5 is during writing back. In this case, (c) a buffer set 6 stores Write data.

Referring to FIG. 19, (d) when a region used by the buffer set 1 is released, the master control module updates the stage pointer information.

If the buffer set 5 is in the writing back, (e) since data is in the write only buffer 201 or the like, the writing back of the buffer set 5 is suspended, and the processing for transferring buffer set data in the buffer set 5 to the copy target device 120 is started.

If the writing back of the buffer set 5 is completed, the staging is performed in which the buffer set data in the buffer set 5 is read out from the save buffer 118 and stored in the buffer set 1.

(5) Staging from Save Buffer 118 to Write Only Buffer 201

FIGS. 20A and 20B are flowcharts briefly illustrating the staging according to this embodiment. The processing illustrated in FIGS. 20A and 20B specifically describes the processing in S1117 a to S1119 a illustrated in FIG. 11B.

In S2000 a, if the release processing for the old generation is completed, the master control module in the copy source device 110 shifts the processing to S2001 a.

In S2001 a, the master control module determines a generation subjected to the staging. For example, the master control module refers to the stage pointer information, increments the generation stored in the stage pointer information by 1, and newly determines the incremented generation as the generation subjected to the staging. The generation subjected to the staging is called “staging subject generation.” In the processing illustrated in FIGS. 20A and 20B, a buffer set acquired in the processing in S1113 a in FIG. 11B and used for the staging is called “staging target.”

In S2002 a, the master control module checks whether a region of the staging target of the staging subject generation waits for the release processing. If the region of the staging target waits for the release processing (S2002 a, YES), the master control module shifts the processing to S2003 a.

In S2003 a, the master control module sets the generation obtained by adding 1 to the staging subject generation as a new staging subject generation. The master control module shifts the processing to S2002 a.

In S2002 a, if the region of the staging target does not wait for the release processing (S2002 a, NO), the master control module shifts the processing to S2004 a.

In S2004 a, the master control module checks whether the staging target is during the transferring. If the staging target is in transferring (S2004 a, YES), the master control module shifts the processing to S2003 a.

In S2004 a, if the staging target is not during the transferring (S2004 a, NO), the master control module shifts the processing to S2005 a.

In S2005 a, the master control module checks whether the staging subject generation is during the staging. If the staging subject generation is during the staging (S2005 a, YES), the master control module shifts the processing to S2003 a.

In S2005 a, if the staging subject generation is not during the staging (S2005 a, NO), the master control module shifts the processing to S2006 a.

In S2006 a, the master control module checks whether the staging subject generation is during the writing back. If the staging subject generation is during the writing back (S2006 a, YES), the master control module shifts the processing to S2007 a.

In S2007 a, the master control module suspends the writing back thereof, and requests the other control modules included in the copy source device 110 for the suspension of the writing back.

In S2001 b, when each of the other control modules receives the request from the master control module, the control module suspends the writing back. Then, the control module notifies completion of the suspension of the writing back to the master control module.

In S2008 a, the master control module checks whether the master control module has received replies from all requested control modules. If there is a control module without a reply (S2008 a, NO), the master control module repeats the processing in S2008 a.

In S2008 a, if the master control module has received the replies from all requested control modules (S2008 a, YES), the master control module shifts the processing to S2009 a, and ends the staging.

In S2006 a, if the staging subject generation is not during the writing back (S2006 a, NO), the master control module shifts the processing to S2010 a.

In S2010 a, the master control module checks whether the staging target is during the storage processing for Write data etc. If the staging target is during the storage processing (S2010 a, YES), the master control module shifts the processing to S2011 a, and ends the staging.

In S2010 a, if the staging target is not during the storage processing for the Write data etc. (S2010 a, NO), the master control module shifts the processing to S2012 a.

In S2012 a, the master control module judges whether the rebuilding is performed for an individual save buffer, which stores the staging subject generation. The master control module determines that the rebuilding is performed for the individual buffer, which stores the staging subject generation, if the flag for the disk access stop mode is ON (S2012 a, YES), the master control module shifts the processing to S2013 a.

In S2013 a, the master control module suspends the staging. The master control module shifts the processing to S2014 a. In S2014 a, the master control module waits for completion of the rebuilding for the individual save buffer, which stores the staging subject generation. Then, if the completion of the rebuilding is detected by interruption or the like, the master control module starts the processing from S2015 a.

In S2012 a, if the flag for the disk access stop mode is OFF, the master control module determines that the rebuilding is not performed for the individual buffer, which stores the staging subject generation (S2012 a, NO). In this case, the master control module shifts the processing to S2015 a.

In S2015 a, the master control module sets the rebuild stop mode. In this embodiment, the flag for the rebuild stop mode is turned ON.

The master control module shifts the processing to S2016 a, and checks whether the staging subject generation is already stored in the staging target previously acquired by the processing in S1113 a in FIG. 11B.

If the staging subject generation is stored in the staging target (S2016 a, YES), the master control module shifts the processing to S2024 a, and ends the staging. If the staging subject generation is not stored in the staging target (S2016 a, NO), the master control module shifts the processing to S2017 a.

In S2017 a, the master control module acquires the number of buffer sets used for the staging or transferring. The master control module compares the number of buffer sets in use with the predetermined threshold, for example, the value that is 50% the total number of buffer sets. If the number of buffer sets in use is the threshold or larger (S2017 a, YES), the master control module shifts the processing to S2024 a, and ends the staging. If the number of buffer sets in use is not the threshold or larger (S2017 a, NO), the master control module shifts the processing to S2018 a.

In S2018 a, the master control module stages the staging subject generation as follows.

The master control module calculates an address of an individual save buffer, in which the staging subject generation is stored, from the save buffer management table 500. The master control module acquires buffer data, a BIT, and buffer set information from the calculated address.

The master control module stores the acquired buffer data, the BIT, and the buffer set information in the individual buffer, the BIT storage unit, and the buffer set information storage unit 202, corresponding to the buffer set indicated by the staging subject buffer set ID. Similar processing is performed for each of the other control modules in the copy source device 110.

If the save buffer assigned to the control module has a continuous address space, an address of the individual save buffer can be obtained by adding “(staging subject generation−1)×individual save buffer size” to “leading address of save data” set in the save buffer management table 500.

In S2019 a, the master control module requests each of the other control modules to acquire a staging subject generation from the save buffer 118 and perform the staging like S2018 a.

In S2002 b, each of the other control modules stages the buffer set information and the BIT as follows.

Each of the control modules requested by the master control module acquires the BIT and the buffer set information of the staging subject generation that is requested from the master control module, from the individual save buffer in the save buffer 118 assigned to the control module.

Each of the other control modules stores the BIT and the buffer set information acquired from the individual save buffer of the save buffer 118, in the BIT storage unit 201 b and the buffer set information storage unit 202 included in the control module.

In S2003 b, each of the other control modules refers to the individual save buffer in the save buffer 118 assigned to the control module, and judges whether the individual save buffer has buffer data of the staging subject generation. If the individual save buffer in the save buffer 118 has the buffer data of the staging subject generation (S2003 b, YES), the control module stages the buffer data (S2004 b). When the staging is completed, the control module notifies the completion to the master control module. Then, the control module shifts the processing to S2005 b, and ends the staging.

In S2003 b, if the individual save buffer in the save buffer 118 does not have the buffer data of the staging subject generation (S2003 b, NO), each of the other control modules notifies the completion to the master control module.

In S2020 a, the master control module monitors the notification of the completion until the master control module receives replies from all requested control modules. If the master control module has received the replies from all requested control modules (S2020 a, YES), the master control module shifts the processing to S2021 a.

In S2021 a, the master control module deactivates the rebuild stop mode. In particular, the master control module turns OFF the flag for the rebuild stop mode.

In S2022 a, the master control module judges whether there is a rebuild queue for the save buffer 118. In particular, the master control module judges whether there is a rebuild queue for the individual save buffer, which stores the staging subject generation. If there is the rebuild queue for the save buffer 118 (S2022 a, YES), the master control module shifts the processing to S2023 a. The master control module executes the rebuild processing. Then, the master control module shifts the processing to S2105 in FIG. 21 (described later).

In S2022 a, if there is no rebuild queue (S2022 a, NO), the master control module shifts the processing to S2024 a, and ends the staging.

(6) Rebuilding for Save Buffer 118

FIG. 21 is a flowchart illustrating the rebuild processing for the save buffer 118 according to this embodiment.

For example, when the master control module detects a failure or the like of the disk device of the save buffer 118, the master control module shifts the processing to S2100 and starts the rebuild processing.

In S2101, the master control module acquires the state of the rebuild stop mode, that is, the setting of the flag for the rebuild stop mode.

In S2102, if the flag for the rebuild stop mode is ON (S2102, YES), the master control module determines that the rebuild stop mode is active, and shifts the processing to S2103.

The master control module suspends the rebuilding (S2103), and waits for the deactivation of the rebuild stop mode (S2104). Then, if the rebuild stop mode is deactivated, for example, the master control module shifts the processing to S2105, and starts the rebuilding.

In S2105, the master control module selects one of regions in the disk device that requires the rebuild processing due to a failure or the like, from the disk device that configures the save buffer 118. The selected region is called “rebuild subject region.” The rebuild processing according to this embodiment is performed for the disk device on the basis of a region with a given size, for example, on the basis of an individual save buffer.

In S2106, the master control module judges whether data is saved in the rebuild subject region. If data is not saved in the rebuild subject region (S2106, NO), the master control module shifts the processing to S2111. If data has been saved in the rebuild subject region (S2106, NO), the master control module shifts the processing to S2107.

In S2107, the master control module judges whether the rebuild processing is executed. For example, the master control module judges the execution of the rebuild processing by taking into account the following information.

(a) Region size that allows new generation to be saved even during rebuilding

(b) I/O increase amount of adjacent generation

(c) Time required for rebuild processing for single rebuild subject region (average time for rebuild processing except first rebuild processing)

In particular, the master control module judges whether the rebuild processing is executed in accordance with whether an individual buffer of an unused buffer set in the buffer set management table has at least a free space with a region size (=Buffer_(Free)) obtained by the following calculation.

(a) An I/O amount of a generation older than the current generation by 2 generations (=I/O_(t-2)) and an I/O amount of a generation older than the current generation by 1 generation (=I/O_(t-1)) are acquired from the stored number of I/O in the buffer set information storage unit 202. Then, an I/O increase amount is obtained.

(b) A buffer change time (=ChgTime) from the generation older than the current generation by 2 generations to the generation older by 1 generation is acquired.

(c) The I/O increase amount per a unit time (=I/O_(ChgTime)) is calculated by the following expression.

$\begin{matrix} {{I/O_{chgTime}} = \frac{{I/O_{t - 1}} - {I/O_{t - 2}}}{ChgTime}} & (1) \end{matrix}$

(d) The time required for the rebuild processing for a single rebuild subject region (=RebuildTime) is multiplied by the I/O increase amount per a unit time (=I/O_(ChgTime)) by the following expression. Thus, the I/O amount during the rebuild processing for the single rebuild subject region (=I/O_(Rebuild)) is obtained. I/O _(Rebuild)=RebuildTime×I/O_(chgTime)  (2)

(e) The region size capable of saving new generations, even if the rebuilding is in operation, is obtained by the following expression. Buffer_(free)≧3×I/O _(Rebuild)  (3)

In this embodiment, the value of Buffer_(Free) is triple the value of I/O_(Rebuild) as illustrated in Expression (3). However, the value of Buffer_(Free) may be double or quadruple the value of I/O_(Rebuild).

If the individual buffer of the unused buffer set in the buffer set management table has the free region with the region size Buffer_(Free) obtained by the above processing (S2107, YES), the master control module shifts the processing to S2108. If the individual buffer of the unused buffer set in the buffer set management table does not have the free region with the region size Buffer_(Free) (S2107, NO), the master control module shifts the processing to S2111.

In S2108, the master control module turns ON the flag for the disk access stop mode. In particular, the master control module turns ON the flag for the disk access stop mode stored in the memory in the master control module. The disk access stop mode is a mode that stop access to the save buffer 118, for example, that stops the writing back or staging.

The master control module checks the disk access stop mode every time when an access is made to the save buffer 118, i.e., every time when the writing back or staging is performed. If the disk access stop mode is ON, the access to the disk, i.e., the writing back or staging is suspended.

In S2109, the master control module executes the rebuild processing. When the rebuild processing is completed, the master control module turns OFF the disk access stop mode. In particular, the master control module turns OFF the flag for the disk access stop mode (S2110).

In S2111, the master control module judges whether there is a process queue for the access to the save buffer 118, i.e., a process queue for the writing back or staging. For example, the access to the save buffer 118 made when the disk access stop mode is ON may be managed with a hold queue or the like.

If there is the process queue for the access to the save buffer 118 (S2111, YES), the master control module shifts the processing to S2112. If there is no process queue for the access to the save buffer 118 (S2111, YES), the master control module shifts the processing to S2113.

In S2112, the master control module executes the disk access to the save buffer 118, i.e., executes the writing back or staging, which is in a queue.

In S1213, the master control module judges whether the rebuild processing has been executed for all individual save buffers in the disk device. The judgment does not take into account the region whose rebuild subject region has no saved data.

If the rebuild processing is completed for all individual save buffers (S2113, YES), the master control module shifts the processing to S2114, and ends the rebuild processing. If a region without the rebuild processing remains (S2113, NO), the master control module shifts the processing to S2101.

FIG. 22 is a flowchart illustrating specific processing of the matching processing (S1111 a) illustrated in FIG. 11B. FIG. 22 illustrates specific processing for the master control module and the other control modules included in the copy source device 110.

In S2201 a, the master control module refers to the unused buffer ID storage unit 206. The master control module checks whether the number of unused buffer IDs stored in the unused buffer ID storage unit 206 is a number required for the matching with copy source IDs included in the buffer set information stored in the buffer set information storage unit 202.

In S2201 a, if the required number of unused buffer IDs is not recognized (S2201 a, NO), the master control module shifts the processing to S2202 a. The master control module waits for unused buffer notification from the copy target device 120 in S2202 a. If the master control module receives the unused buffer notification, the master control module shifts the processing to S2201 a.

In S2201 a, if the required number of unused buffer IDs is recognized (S2201 a, YES), the master control module shifts the processing to S2203 a.

In S2203 a, the master control module acquires the required number of unused buffer IDs from the unused buffer ID storage unit 206. The master control module associates copy target IDs included in the buffer set information previously stored in the buffer set information storage unit 202, with the acquired unused buffer IDs. Accordingly, the copy source buffer is matched with the copy target buffer.

When the matching processing is ended, the master control module requests the other control modules to perform multiplexing the buffer set information.

In S2201 b, when each of the other control modules receives the request for multiplexing the buffer set information from the master control module, the control module performs the multiplexing for the buffer set information. Herein, the multiplex processing for the buffer set information is processing for causing all control modules included in the copy source device 110 or the copy target device 120 to hold the same buffer set information.

For example, each of the other control modules acquires the buffer set information with the matching processing performed in S2203 a from the master control module. Then, the control module reflects the acquired buffer set information to the buffer set information storage unit 202 included in the control module.

When the multiplex processing for the buffer set information in S2201 b is ended, each of the other control modules notifies completion of the multiplex processing for the buffer set information to the master control module.

In S2205 a, the master control module checks whether the master control module has received replies from all control modules requested for the multiplex processing for the buffer set information. If the master control module has received the replies from all control modules (S2205 a YES), the master control module ends the processing for the assignment for the copy target buffer (S2206 a), and shifts the processing to S1112 a illustrated in FIG. 11B.

The copy source device 110 according to this embodiment includes a plurality of memories such as the memory 200 illustrated in FIG. 2 and the save buffer 118.

If the use rate of buffer sets using the plurality of memories becomes a predetermined level or higher, the copy source device 110 performs the writing back in which the buffer set data is saved to the save buffer 118.

For example, when line performance between the copy source device 110 and the copy target device 120 is low and the copy source device 110 receives Write I/O commands one after another from the host 150, if the use rate of buffer sets becomes the predetermined level or higher, the copy source device 110 saves the buffer set data to the save buffer 118.

When the copy source device 110 completes the transfer and expansion processing for the buffer set data to the copy target device 120, the copy source device 110 releases the region where the buffer set data is stored, and stages the buffer set data which has been saved to the save buffer 118, into the released region. The copy source device 110 transfers the buffer data to the copy target device 120.

As described above, with the copy source device 110 according to this embodiment, even if the transfer processing for data is delayed such as when the line performance between the copy source device 110 and the copy target device 120 is low, the shortage of a buffer set can be prevented from occurring. As a result, the copy source device 110 can perform the remote copy that ensures the ordering even if the transfer processing for data is delayed.

A similar advantage can be attained even if the transfer processing for data is delayed such as when the line performance is not uniform and is unstable or when a data update amount by Write I/O etc. exceeds the capacity of the write only buffer 201 in the copy source device 110.

Further, with the copy source device 110 according to this embodiment, if the rebuilding is required due to a failure or the like of the save buffer 118 having the redundant configuration, the execution of the rebuilding is controlled in accordance with the free space and the I/O load of the write only buffer 201.

Accordingly, the disk access to the save buffer 118, i.e., the writing back or staging does not interfere with the rebuilding for the save buffer 118, and hence, the operation for saving the buffer set data in the save buffer 118 can be prevented from being delayed. Thus, even if the operation for saving the buffer set data to the save buffer 118 is delayed and Write I/O is received one after another, the shortage of a buffer set can be prevented from occurring.

Consequently, even through the rebuilding is performed for the save buffer 118, the remote copy that ensures the ordering can be preformed. Also, the redundancy of the save buffer 118 can be recovered while the remote copy that ensures the ordering is performed.

Further, the copy source device 110 does not perform the rebuilding for a rebuild subject region if this rebuild subject region have no saved data. Thus, the load of the rebuilding can be reduced.

In conventional remote copy processing, matching processing between copy source IDs and copy target IDs is performed when buffer set information is generated. However, in the remote copy processing according to this embodiment, the matching processing is not performed in S1102 a, but is performed immediately before the transfer processing after completion of the storage processing to the buffer (S1111 a).

Thus, the storage processing for data can be performed simultaneously with the transfer processing for buffers other than buffers relating to the transfer processing. All buffers including the write only buffers 201 and the buffer set information storage units 202 in the copy source device 110 can be efficiently used. For example, data relating to Write I/O from the host 150 can be stored until the capacity of the buffers in the copy source device 110 is used up.

As a result, regarding the buffers to be used for the remote copy that ensures the ordering, even if the buffers included in the copy target device 120 is fewer than the buffers included in the copy source device 110, the buffers in the copy source device 110 can be effectively used.

Also, if the copy source device 110 and the copy target device 120 are disconnected from one another, for example, because a certain trouble occurs in the network therebetween, Write data can be stored as much as possible unless the capacity of the buffers in the copy source device 110 is used up. Thus, as long as the disconnected state is addressed before the buffers are used up, the remote copy processing that ensures the ordering does not have to be suspended. As a result, reliability and stability of the remote copy processing can be increased.

All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiment of the present inventions have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention. 

What is claimed is:
 1. A storage apparatus connected to a storage device, comprising: a storage; a memory to store data to be copied to the storage device; a plurality of save buffers to temporarily save the data stored in the memory, the data saved in one of the plurality of save buffers being capable of being rebuilt on the basis of the saved data stored in the rest of the save buffers; and a processor to execute: receiving a write request including the data to be stored in the storage apparatus from an external device, storing the data included in the write request to the storage, storing the data included in the write request to the memory, copying the data stored in the memory to the storage device, saving the data stored in the memory to the save buffer when a rate of use of the memory which stores the data of the copying is greater than a predetermined rate, writing the saved data stored in the save buffer to the memory when a rate of use of the memory which stores the data of the copying is not greater than the predetermined rate, detecting a failure of the one of the plurality of save buffers, and rebuilding the saved data stored in the one of the plurality of save buffers on the basis of state information indicating a state of the plurality of save buffers, the state information including an in-use state and an unused state.
 2. The storage apparatus according to claim 1, wherein the state information is a size of the plurality of save buffers available.
 3. The storage apparatus according to claim 1, wherein the processor receives a plurality of write requests, and the state information is an amount of the data included in the write requests.
 4. The storage apparatus according to claim 1, wherein the processor executes the rebuilding after the saving and the writing are completed.
 5. The storage apparatus according to claim 1, wherein the processor executes one of the saving and the writing after the rebuilding is completed.
 6. The storage apparatus according to claim 1, wherein the processor skips the data stored in the plurality of save buffers when the data is not the saved data.
 7. A method of controlling a processor included in a storage apparatus connected to a storage device, including a storage, a memory for storing data to be copied to the storage device, and a plurality of save buffers for temporarily saving the data stored in the memory, the data saved in one of the plurality of save buffers being capable of being rebuilt on the basis of the saved data stored in the rest of the save buffers, the method comprising: receiving a write request including the data to be stored in the storage apparatus from an external device; storing the data included in the write request to the storage module; storing the data included in the write request to the memory; copying the data stored in the memory to the storage device; saving the data stored in the memory to the save buffer when a rate of use of the memory which stores the data of the copying is greater than a predetermined rate; writing the saved data stored in the save buffer to the memory when a rate of use of the memory which stores the data of the copying is not greater than the predetermined rate; detecting a failure of the one of the plurality of save buffers; and rebuilding the saved data stored in the one of the plurality of save buffers on the basis of state information indicating a state of the plurality of save buffers, the state information including an in-use state and an unused state.
 8. The method according to claim 7, wherein the state information is a size of the plurality of save buffers available.
 9. The method according to claim 7, wherein the receiving receives a plurality of write requests, and the state information is an amount of the data included in the write requests.
 10. The method according to claim 7, wherein the rebuilding rebuilds the saved data after the saving and the writing are completed.
 11. The method according to claim 7, wherein one of the saving saves the data and the writing writes the saved data after the rebuilding is completed.
 12. The method according to claim 7, further comprising skipping the data stored in the plurality of save buffers when the data is not the saved data. 